This invention relates generally to button manufacture, and more particularly to an improved pivot tack button
In the garment and furniture trades, pivot tacks of the type with which the present invention is concerned are inserted into the back of a covered button and are designed to lock with the button by rolling over the shank of the tack as the shank engages the steel "roof" of the insert within the button shell. In theory the gradual pressing of the tack into assembled relationship with the remainder of the button comes about by the rolling over of the shank of the tack so that the roll-over or curl supposedly formed draws the head of the tack tightly up against the fabric to which the button is being attached and also clinches the button shell and the insert rigidly together.
Presently the known design of pivot tacks provides a uniform diameter shank with a very short taper at the tip of the shank so that the point will easily penetrate the materials and enter the pivot back or button shell easily. Generally speaking, the tacks are made from wire stock with the result that as the covered button and tack are moved relatively toward one another during the button installation process the engagement of the tip of the tack with the surface of the insert causes the tack to bend sideways and only partially curl. As a result the shank of the tack does not fully contact the back member thus causing a looseness and possible separation of the button parts. If the button components are not clinched together firmly the button falls away from the garment or furniture. Thus, a uniform diameter shank and a short taper at the tip results in a structure that has a tendency to crush or buckle rather than curl uniformly inside the button to lock the parts together. Actually, the buckling of the tack shank results in a loose attachment that looks tight but can easily come apart when handled.
Another known form of pivot tack uses a taper which is longer than the typical taper confined to the point of the tack shank. However, the insert within the button and against which the tack shank impinges includes a dimple centered in order to try to deflect the shank of the tack sideways and cause it to curl. Instead, the shank often buckles.
In general the foregoing approaches to the problem of locking the button parts together have not produced satisfactory results.